1. Field of the Invention
The present invention relates to an ink jet recording device having a monitor function for monitoring ink droplet generating conditions.
2. Related Art
There has been proposed a line scanning type ink jet printer, capable of printing images on an elongated uncut recording sheet at a high printing speed. This type of printer includes a head having a plurality of nozzles and an elongated width covering over the entire width of the recording sheet. When printing images, ink droplets are ejected from the nozzles, charged, and deflected, and then impact on the recording sheet that is being fed at a high speed in its longitudinal direction. The impact positions of the ejected ink droplets on the recording sheet are controlled based on a recording signal. By controlling the impact positions of the ink droplets and the feed of the recording sheet, a desired image is formed on the recording sheet.
There are two types of line scanning type ink jet printer. One includes a continuous ink jet head, and the other includes an on-demand ink jet head.
Although, the printer with the on-demand ink jet head is slow in printing speed compared with the printer with the continuous ink jet head, the on-demand ink jet head requires a simple ink system, and so is well suited for a general-purpose high-speed printer.
When a nozzle of ink jet printers becomes defective, a part of an image corresponding to the defective nozzle may be left out or may have an unevenness in ink density, resulting in degradation of image quality. Therefore, in order to maintain a high quality of images, it is necessary to monitor the ink ejection condition of each nozzle.
Japanese Patent-Application Publication No. SHO-61-53053 discloses an ink jet printer having a monitor function for monitoring ink droplet generation. After an ink-droplet-charging signal is generated to charge ink droplets for a certain period of time, a charged-amount-detection signal is detected for a certain period of time so as to detect charging condition of the ink droplets. A changeable amplifying means amplifies the charged-amount-detection signal at an amplification rate. An amplification-rate-control-signal generation circuit generates and outputs an amplification-rate-control signal to control the changeable amplifying means to change the amplification rate. Specifically, the amplification-rate-control signal controls the changeable amplifying means to set to a lower amplification rate when the ink-droplet charging signal is being generated, and to a higher amplification rate when the charged-amount-detection signal is being detected. In this way, the charged amount, i.e., charging condition of ink droplet, is detected while preventing a detection error, because electrical noise is not amplified other than when the charged amount-detection signal is being detected.
However, in the above printer, because a pulse-shaped high voltage signal is used as the ink-droplet charging signal, its influence is reflected in the charged-amount detection signal, which is a weak signal, so the signal-to-noise ratio (SNR) becomes small.
It is an object of the present invention to overcome the above problems, and also to provide an ink jet recording device capable of detecting the ink droplet generation condition with high SNR.
In order to achieve the above and other objective, there is provided an ink jet recording device including a head formed with a nozzle and selectively ejecting an ink droplet from the nozzle, a deflecting means for deflecting a flying direction of the ink droplet ejected from the nozzle, the deflecting means including a first electrode and a second electrode, a mode selecting means for selecting one of a first mode and a second mode, an applying means for applying a direct voltage to the first electrode and another direct voltage to the second electrode throughout the first mode and the second mode, the direct voltage differing from the another direct voltage, and a detection means for detecting a quantity of electricity relating to an electric discharge flowing through the first electrode in the second mode.
There is further comprising a control method for controlling an ink jet recording device. The control method comprises the steps of a) selecting a first mode, b) applying a direct voltage to a first electrode and another direct voltage to a second electrode throughout the first mode and a second mode, the direct voltage differing from the another direct voltage, c) ejecting an ink droplet from a nozzle of an ink jet head in the first mode, d) switching from the first mode to the second mode, and e) detecting a quantity of electricity relating to an electric discharge flowing through the first electrode.